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Abstract:

A surface treatment method of a subject body is comprised steps of:
packing and pressurizing powder including an electrically conductive
material in a mold so as to obtain a plurality of compressed powder
bodies; joining the plurality of compressed powder bodies together by
arranging the plurality of compressed powder bodies to be mutually in
close contact and applying isostatic pressure on the arranged compressed
powder bodies; sintering the joined compressed powder bodies so as to
obtain a sintered body; and carrying out a discharge surface treatment by
bringing the sintered body close to a subject body and generating
electric discharge.

Claims:

1. A production method of an electrode for a discharge surface treatment
comprising the steps of: packing and pressurizing powder including an
electrically conductive material in a mold so as to obtain a plurality of
compressed powder bodies; joining the plurality of compressed powder
bodies together by arranging the plurality of compressed powder bodies to
be mutually in close contact and applying isostatic pressure on the
arranged compressed powder bodies; and sintering the joined compressed
powder bodies so as to obtain a sintered body.

2. The production method of claim 1, further comprising the step of
preliminary isostatic pressure, wherein isostatic pressure is applied to
each compressed powder body individually.

3. The production method of claim 2, wherein the isostatic pressure in
the step of joining is identical to pressure in the step of packing and
pressurizing, and a second isostatic pressure in the step of preliminary
isostatic pressure is lower than the isostatic pressure in the step of
joining.

4. An electrode for a discharge surface treatment produced by the
production method of claim 1.

5. A surface treatment method of a subject body, comprising the steps of:
packing and pressurizing powder including an electrically conductive
material in a mold so as to obtain a plurality of compressed powder
bodies; joining the plurality of compressed powder bodies together by
arranging the plurality of compressed powder bodies to be mutually in
close contact and applying isostatic pressure on the arranged compressed
powder bodies; sintering the joined compressed powder bodies so as to
obtain a sintered body; and carrying out a discharge surface treatment by
bringing the sintered body close to a subject body and generating
electric discharge.

7. The surface treatment method of claim 6, wherein the isostatic
pressure in the step of joining is identical to pressure in the step of
packing and pressurizing, and a second isostatic pressure in the step of
preliminary isostatic pressure is lower than the isostatic pressure in
the step of joining.

Description:

TECHNICAL FIELD

[0001] The present invention relates to an electrode for utilizing
electric discharge to form a coating or a deposition on a subject, and a
method for forming a coating or a deposition therewith.

BACKGROUND ART

[0002] To bring a non-consumable electrode close to a subject body in oil
or in the air and generate electric discharge therebetween, the subject
body can be machined. This art is in general referred to as electric
spark machining, and is known to enable precise machining and formation
of complex shapes. Under certain conditions, such as those where a
consumable electrode such as a compressed powder body is used instead of
a non-consumable electrode, or any, consumption of the electrode
preferentially occurs instead of machining the subject body. A material
constituting the electrode or its reaction result at this time covers an
area on the subject body opposed to the electrode, thereby enabling
surface treatment of the subject body. A related art is disclosed in an
International Publication WO 99/58744. In the publication, this art is
referred to as "discharge surface treatment".

DISCLOSURE OF INVENTION

[0003] As being understood from the above description, the subject of a
discharge surface treatment is essentially limited to an area opposed to
the electrode. This property is one of advantages of the discharge
surface treatment as it enables localized surface treatment. On the other
hand, in a case where surface treatment should be carried out on a large
area with uniformity, it could be a disadvantage.

[0004] The present invention has been achieved in view of the
aforementioned problem and its purpose is to provide an art which enables
large area surface treatment while it is based on discharge surface
treatment.

[0005] According to a first aspect of the present invention, a production
method of an electrode for a discharge surface treatment is comprised of
steps of: packing and pressurizing powder including an electrically
conductive material in a mold so as to obtain a plurality of compressed
powder bodies; joining the plurality of compressed powder bodies together
by arranging the plurality of compressed powder bodies to be mutually in
close contact and applying isostatic pressure on the arranged compressed
powder bodies; and sintering the joined compressed powder bodies so as to
obtain a sintered body.

[0006] Preferably, the production method further includes a step of
preliminary isostatic pressure, wherein isostatic pressure is applied to
each compressed powder body individually. More preferably, in the
production method, the isostatic pressure in the step of joining is
identical to pressure in the step of packing and pressurizing, and a
second isostatic pressure in the step of preliminary isostatic pressure
is lower than the isostatic pressure in the step of joining.

[0007] According to a second aspect of the present invention, a surface
treatment method of a subject body is comprised of steps of: packing and
pressurizing powder including an electrically conductive material in a
mold so as to obtain a plurality of compressed powder bodies; joining the
plurality of compressed powder bodies together by arranging the plurality
of compressed powder bodies to be mutually in close contact and applying
isostatic pressure on the arranged compressed powder bodies; sintering
the joined compressed powder bodies so as to obtain a sintered body; and
carrying out a discharge surface treatment by bringing the sintered body
close to a subject body and generating electric discharge.

[0008] Preferably, the surface treatment method further includes a step of
preliminary isostatic pressure, wherein isostatic pressure is applied to
each compressed powder body individually. More preferably, in the surface
treatment method, the isostatic pressure in the step of joining is
identical to pressure in the step of packing and pressurizing, and a
second isostatic pressure in the step of preliminary isostatic pressure
is lower than the isostatic pressure in the step of joining.

BRIEF DESCRIPTION OF DRAWINGS

[0009]FIG. 1 is a drawing explaining a production method of an electrode
in accordance with an embodiment of the present invention, which
illustrates a step of obtaining a compressed powder body by pressurizing.

[0010]FIG. 2 is a drawing explaining a step in the production method in
which isostatic pressure is applied to each compressed powder body
individually.

[0011]FIG. 3 is a drawing explaining a step in the production method in
which a plurality of compressed powder bodies is arranged and then joined
together.

[0012]FIG. 4 is a perspective view illustrating an example of a plurality
of compressed powder bodies arranged to be mutually in close contact.

[0013]FIG. 5 is a schematic drawing showing a step of sintering in the
production method.

[0014]FIG. 6 is a schematic drawing showing a discharge surface treatment
method in accordance with the present embodiment.

[0015]FIG. 7 is a schematic drawing showing a mode of the discharge
surface treatment method, in which an electrode and a subject body are
installed in an electric spark machine.

BEST MODE FOR CARRYING OUT THE INVENTION

[0016] Throughout the present specification and the appended claims, the
term "discharge surface treatment" is defined and used as an act of
utilizing electric discharge in an electric spark machine to consume an
electrode instead of machining a subject body, and adhering a material
constituting the electrode, or a reaction product between the material
constituting the electrode and a machining liquid or a machining gas,
onto the subject body as a coating.

[0017] An embodiment of the present invention will be described
hereinafter with reference to the appended drawings.

[0018] In the present embodiment, first a consumable electrode for a
discharge surface treatment is produced.

[0019] As a material for the consumable electrode, electrically conductive
powder is preferable. The electrically conductive powder may, as a whole,
consist of any metal or any semiconductor substance, or alternatively a
mixture of any metal or a semiconductor substance and the other substance
such as a proper ceramic. Which to choose is determined in accordance
with properties required for a coating to be formed on a subject body.

[0020] Preferably a binder is added to the powder and then appropriately
mixed thereto. As examples of the binder, paraffin, carnauba wax,
polypropylene, polyethylene, acrylic resin, methacrylic resin, and acetal
resins can be exemplified, however, any substance which helps loose
bonding among powder particles and does not leave undesirable residual
substances after sintering may be applicable.

[0021] Powder 7 with the binder or such added thereto is, as shown in FIG.
1(a), packed in a mold 9. The mold 9 is comprised of a die 11 of a
cylindrical shape for example, an upper punch 13 and a lower punch 15
both of which fit in an inner hole 11h of the die 11. The punches 13, 15
are slidable relative to the inner hole 11h and also establish a proper
fit with the inner hole 11h so as to prevent leakage of the powder 7 when
being pressurized.

[0022] The mold 9 with the powder 7 packed therein is charged in a proper
press machine. The upper and lower punches 13, are pressurized by means
of rams 17, 19 of the press machine so that the powder 7 packed in the
mold 9 is pressurized. By this pressurizing, the powder 7 is as shown in
FIG. 1(b) aggregated, thereby obtaining a compressed powder body 21 which
does not readily collapse. The shape of the compressed powder body 21 can
be properly regulated by the shape of the inner hole 11h and the amount
of the powder 7, and is, for example, of a quadrangular prism shape with
dimensions of 15 (D)×8 (W)×100 (L) mm3. Of course, other
various shapes such as a hexagonal prism shape are possible. This step is
reciprocally carried out and then a plurality of compressed powder bodies
21 is obtained.

[0023] Preferably, preliminarily before subsequent steps, a process to
apply isostatic pressure, such as cold isostatic press (CIP), is
individually carried out on the compressed powder bodies 21. More
specifically, each compressed powder body 21 is, as shown in FIG. 2(a),
individually sealed in a thin rubber bag 23. Any proper elastic material
instead of rubber may be utilized. The compressed powder body 21 along
with the bag 23 in this state is, as shown in FIG. 2(b), immersed in
liquid L in a pressure vessel 25 and then isostatically pressurized. This
step improves uniformity of density of the compressed powder body 21 and
accordingly improves uniformity of a final product.

[0024] Preferably the isostatic pressure in the preliminary isostatic
pressure step is lower than a pressure in the step of pressurizing the
powder 7. Such isostatic pressure is beneficial in prevention of
deformation of the compressed powder body 21.

[0025] Next the compressed powder bodies 21 are arranged to be mutually in
close contact. FIG. 3(a) illustrates one of such examples. A mode in
which compressed powder bodies 21 having a common length are arranged in
parallel may be applied, and also they may contain short compressed
powder bodies 21 arranged in series. The number of the compressed powder
bodies 21 can be increased or reduced as necessary. Preferably, they are
brought into a state in which ends thereof are made flush with each other
as shown in FIG. 3(a).

[0026] The plurality of compressed powder bodies 21 is sealed in a bag 27
of a rubber or such, and CIP is as shown in FIG. 3(b) carried out
thereon. Alternatively, hot isostatic press (HIP) instead of CIP may be
applied. In a case of applying HIP, a heating condition may be set up so
that presintering in the compressed powder bodies 21 properly progresses.
Alternatively it may be modified so that a sintering step as described
later is simultaneously carried out in HIP. By applying isostatic
pressure by means of the liquid L in the pressure vessel 25, the
plurality of compressed powder bodies 21 is joined together to obtain a
joined body 29 as shown in FIG. 4.

[0027] Preferably, the isostatic pressure applied on the plurality of
compressed powder bodies 21 is identical to pressure in the step of
pressurizing the powder V. Such isostatic pressure is beneficial in
promoting joining while preventing deformation of the compressed powder
bodies 21.

[0028] While the joined body 29 is composed of the plurality of compressed
powder bodies 21, the compressed powder bodies 21 are mutually joined and
thus the joined body 29 does not readily collapse. As keeping this state,
the joined body 29 is as shown in FIG. 5 introduced into a heating
furnace 31.

[0029] As the heating furnace 31, any furnace having ability of atmosphere
control is preferable for the purpose of preventing oxidation. Preferably
the atmosphere in the heating furnace 31 is set to be non-oxidative. By
way of example of a non-oxidative atmosphere, a vacuum below 10-1 Pa
and inert atmospheres by inert gases such as nitrogen or argon can be
exemplified.

[0030] The heating furnace 31 is further comprised of a proper heating
means 33 such as a carbon heater. By heating the joined body 29 by means
of the heating means 33, sintering progresses. In regard to the heating
temperature, higher temperatures are advantageous in view of promotion of
sintering, however, temperatures sufficiently lower than a melting point
of the material constituting the power 7 are preferable in view of
preventing a phenomena in that the electrode becomes hardly consumed as
sintering overly progresses. Thus, as the heating temperature, 0.5-0.8 Tm
can be exemplified where Tm (degrees C.) is a melting point of the
material constituting the powder 7.

[0031] As sintering progresses, additives such as the binder contained in
the compressed powder bodies 21 are evaporated and then disappear, and
further firm bonds among the particles in the powder appear. Moreover
also among the plurality of compressed powder bodies 21, firm bonds
appear. The sintered body as a result becomes a single solid as a whole.
To utilize it as an electrode for a discharge surface treatment,
sintering should be stayed at a stage where openings among the particles
do not disappear. According to the aforementioned process, in
considerable cases, the openings among the particles do not appear
without taking any particular measures, thereby giving a porous sintered
body.

[0032] Meanwhile joining and sintering may be simultaneously carried out,
as described already, by means of HIP, instead of independent execution
of the step of sintering and the step of joining.

[0033] After finishing the sintering, the sintered body is properly cooled
so as to prevent excessive thermal shock thereon. The sintered body is
thereafter taken out of the heating furnace 31. The sintered body as
shown in FIG. 6 can be utilized as an electrode 1 for a discharge surface
treatment.

[0034] A discharge surface treatment with using the electrode formed of
the sintered body as produced in a way as described above will be
described with reference to FIGS. 6 and 7 hereinafter. While the
discharge surface treatment will be applicable to various products, FIG.
6 illustrates an example in that a subject body 3 of the surface
treatment is a rotor blade of a gas turbine engine and an area of the
subject is a tip end of the rotor blade.

[0035] Referring to FIG. 7, an electric spark machine 41 is comprised of
an electrically conductive bed 43, a machining bath 45 capable of pooling
a machining liquid F, a power supply 47, and a head 49 to which the
electrode is fixed. The head 49 is capable of going up and down by means
of any proper means, and further the electric spark machine 41 may be
comprised of a servomotor 51 for making the head go up and down. In the
machining bath 45, a non-conductive machining liquid F such as oil is
pooled, and a tip end of the electrode 1 and the subject body 3 are both
immersed in the machining liquid F. Alternatively, in the air or any gas
instead of the liquid F, the discharge surface treatment can be carried
out. The subject body 3 is fixed on the bed 43 so as to allow current
conduction therethrough. Both poles of the power supply 47 are respective
electrically connected to the bed 43 and the head 49, thereby allowing
current conduction from the power supply 47 to the electrode 1 and the
subject body 3.

[0036] In the electric spark machine 41 as described above, the electrode
1 is brought close to a subject area of the subject body 3. Then
electricity is supplied from the power supply 47 and discharge is thereby
generated between the electrode 1 and the subject body 3. Preferably the
supplied electricity is made intermittent so that the discharge is
generated in a pulsed manner. As the electrode 1 is porous as described
above, it undergoes consumption preferentially relative to the subject
body 3, thereby the material constituting the electrode 1, as a coating,
adheres to the subject area on the subject body 3. Alternatively, by
properly selecting the material constituting the electrode 1 and the
machining liquid F, its reaction product may be the coating 5. Part of
energy of the discharge is thrown into the subject area of the subject
body 3 so as to cause local fusion and therefore bonding between the
coating 5 and the subject body 3 is firm. Further, as a part in the
subject body 3 in which the energy of the discharge is thrown is
localized and superficial, the subject body 3 hardly experiences thermal
damage and deformation.

[0037] As the electrode 1 is consumed, a depression 1t as shown in FIG.
6(b) develops on the lower end of the electrode 1. The depression 1t has
a shape corresponding to the subject area of the subject body 3. When
such consumption grows up to a considerable level, it is preferable to
slightly move the electrode 1 or the subject body 3 so as to have a fresh
surface of the electrode 1 opposed to the subject area. FIG. 6(b)
illustrates a state after repeating such processes several times.
Alternatively, instead of slightly moving the electrode 1 or the subject
body 3, it may be preferable to flip it horizontally. FIG. 6(c)
illustrates such an example.

[0038] According to the present embodiment, as plural compressed powder
bodies 21 are individually formed, each compressed powder 21 is accurate
in shape and is further uniform in density. As the electrode 1 is formed
by joining and sintering them, these properties are reflected in the
resultant product, thereby the electrode 1 has high accuracy in shape and
high uniformity. In contrast, in accordance with studies by the present
inventors, when a relatively large-sized electrode is not formed by the
present method but formed directly by molding and sintering, it results
in non-uniformity in density from its periphery toward its center
generates and often deformation by shrinkage around its center. Such a
sintered body is not suitable for an electrode for a discharge surface
treatment in view of its shape and non-uniformity. As compared with such
a situation, the present embodiment is prominently advantageous in
accuracy in shape and uniformity.

[0039] According to the present embodiment, an electrode with accuracy in
shape and uniformity can be constituted even though it is large-sized.
Scalable expansion of its dimensions is enabled while accuracy in shape
and uniformity are retained at high levels. The present embodiment
enables uniform surface treatment on a large area. As it is based on a
discharge surface treatment, one can still enjoy an advantage in that a
surface-treated area is limited within a area opposed to the electrode.

[0040] Although the invention has been described above by reference to
certain embodiments of the invention, the invention is not limited to the
embodiments described above. Modifications and variations of the
embodiments described above will occur to those skilled in the art, in
light of the above teachings.

INDUSTRIAL APPLICABILITY

[0041] An art which enables large area surface treatment is provided while
it is based on a discharge surface treatment.